The translational dynamics of specific cell membrane components will be studied, with particular emphasis placed on the systematic transport processes associated with active cell locomotion. A variety of modern optical methods will be used, principally the recently developed fluorescence photobleaching recovery. Non-radiative fluorescence energy transfer, determined as a function of time and position across the membrane, will also be used as a sensitive measure of microscopic proximity relationships of different cell membrane components. Experiments on whole cells will be supplemented with studies on model membrane systems. The ultimate goal will be an exploration of causal relationships between the molecular composition and organization of a membrane, its fluid dynamics, and specific membrane functions.